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The invention relates generally to fermentation vessels, such as are used in the wine industry, and more particularly to a fermentation vessel that circulates a portion of liquid from the fermentation chamber over the top of the contents in the fermentation chamber.
Red wine is typically made by crushing dark-skinned grapes and extracting color and flavor components from the grape skins and pulp by allowing the crushed grapes, including their juice, to sit for a period of time. This extraction time is followed by a fermentation stage where yeast converts sugar in the grape juice to alcohol and carbon dioxide. The fermentation can also facilitate in extracting flavor and color from the skins. This process is often referred to as xe2x80x9cmacerationxe2x80x9d. The wine or partially fermented grape juice (xe2x80x9cmustxe2x80x9d) is typically pressed from the skins, stems, and other large solids, collectively referred to as pomace, and transferred to a secondary vessel where further processing occurs.
During the extraction period the large solids typically float to the surface of the crushed grapes to form a xe2x80x9ccapxe2x80x9d. This cap can be relatively thick and portions can partially dry out, which diminishes extraction. If fermentation is occurring, the carbon dioxide formed by the yeast can also carry solids to the surface because the gas bubbles nucleate on the solids and carry them to the top of the liquid. Heat is also generated during fermentation and the drier portion of the cap can overheat, generating undesirable flavor components.
Thus, many techniques have been developed to keep the cap moist to improve the extraction of flavor and color. The xe2x80x9cgrape stompxe2x80x9d, for example, is directed at submerging the cap into the must, rather than crushing fresh grapes, as is often thought. Other manual methods exist, such as large plungers that the winemaker can use to push portions of the cap into the must. Many of these methods can be tedious and imprecise. The imprecision can lead to a lack of process control that can affect the quality of the wine produced. Therefore, other methods have been developed to assist in the extraction and fermentation processes of red wine making.
One approach uses a pump-over fermentation tank. One type of pump-over fermentation tank has a pump-over chamber above a fermentation chamber, with a valve in a septum separating the chambers. A pump transfers must from the fermentation chamber into the pump-over chamber, where it accumulates until a disk valve is opened, releasing the must over the cap. If only a little must has accumulated in the pump-over chamber, then the cap is predominately moistened when the valve is opened. If more must has been accumulated, then the flow from the upper chamber to the lower might be sufficient to mix at least some of the cap back into the must.
However, the disk valve tends to divert much of the must from the pump-over chamber to the edge regions of the cap, if not to the sidewall of the fermentation chamber, until the head of liquid in the pump-over chamber diminishes, decreasing the spray radius from the disk valve. Spraying the sidewall of the fermentation chamber precludes spraying the cap with that liquid, and is inefficient in terms of pumping.
Similarly, if mixing of the cap is desired and a large amount of liquid has been accumulated in the pump-over chamber, when the disk valve is opened much of the liquid is merely sprayed on the sidewall of the fermentation tank. The force of this liquid is primarily sideways, rather than directed down at the cap. Thus, this arrangement concentrates the pump-over liquid at the perimeter of the cap, rather than at the cap surface.
A pump-over fermentation tank includes a fermentation chamber separated from a pump-over chamber by a septum. A pump pumps liquid from the fermentation chamber into the pump-over chamber through a pump-over pipe. A chamber valve between the chambers can be closed to separate the chambers and allow accumulation of liquid in the pump-over (upper) chamber and opened to dispense the liquid onto the surface of the contents in the fermentation chamber. In one embodiment, the chamber valve has a movable valve member with diffusers disposed on a perimeter of the movable valve member so as to direct liquid from the pump-over chamber over the surface of the contents in the fermentation chamber. In a particular embodiment, the diffusers are interspersed with notches. In a further embodiment, back diffusers direct liquid from the perimeter of the-movable valve member to the center of the tank:In
In another or further embodiment, the movable member has a tapered face that mates with a valve seat to seal the chamber valve. The tapered valve face self-centers the movable member in the valve seat as the valve is closed. A valve actuator connected to the movable member can open the valve slowly or quickly. In other words, the valve actuator has at least two speeds.
In yet another embodiment of the present invention, a vortex impeller pump is used to pump the liquid from the lower chamber to the upper chamber. The vortex impeller pump is fabricated from stainless steel stock, rather than cast, to provide a smooth interior surface. It is believed this smooth interior surface avoids abrasion of the incidental solids transferred through the pump. In a further embodiment, the vortex impeller pump is powered by a low-speed electric motor. In a 3-phase, 60 Hz system, this low speed motor has a speed of about 1200 rpm, rather than the 1800 rpm of a standard-speed motor.
In a method according to an embodiment of the present invention, the chamber valve can be opened at different speeds to achieve different effects. The valve is opened slowly to irrigate the cap during extraction or fermentation, and can be opened quickly, which is usually done after accumulating liquid in the upper chamber, to mix the cap with the liquid in the lower chamber. In a particular embodiment, the extraction and fermentation processes are automated and controlled by a system controller or computer. The winemaker can program the system-controller to perform a selected number of irrigations over an extraction period. The controller then pauses to allow the winemaker to inoculate the crushed grapes, and enters a command to continue the process. The controller can be programmed to perform a series of irrigations during the fermentation period, and can also be programmed to accumulate must in the upper chamber to be rapidly dumped into the lower chamber, mixing the cap.